An embodiment of the present invention relates generally to a light beam scanning element, and more particularly, to a light beam scanning element having at least one elastomeric support, and methods of manufacturing the same.
In laser-based barcode scanning equipment, and particularly in portable laser-based barcode scanning equipment, a scan component is used to dither a mirror. The moving mirror is used to sweep a laser beam across a barcode target to be read. This component is often called a scan element. A scan element is a critical moving component in portable laser-based barcode readers. Desirable attributes for a scan element are small size, ruggedness, energy efficiency, freedom from beam shifting when held in different orientations, and immunity to unwanted motions of the scan beam when held by an operator.
Conventional hinge-based scan elements are formed from cantilevered beams of plastic film or other flexible materials and are not balanced structures. Several such scan elements are described in U.S. Pat. No. 6,173,895, which suffer from unwanted tilting or drooping of the scan mirror when held in different orientations due to the effects of gravity, especially if the scan mirror and moving magnet are large. Further, flexible film hinges can become permanently distorted if the device is dropped or otherwise exposed to rough handling. Such distortion produces shifted scan lines or scan lines that are no longer straight. Shaft-based scan elements, such as described in U.S. Pat. No. 7,420,721 B2, are also prone to wobble of the scan mirror induced by gravity or operator movement when used in portable hand held applications. The above-described drawbacks are exacerbated by the use of large scan mirrors required for long range scanning.
Beam shifting may also be caused by the addition of an inductive pole piece within the electromagnetic drive coil, (see, e.g., U.S. Pat. No. 7,420,721 B2). The pole piece generates a magnetic bias that can tilt the scan mirror or cause unwanted forces, which result in undesirable speed perturbations of the scan line. Thus, tedious adjustment is needed to ensure proper operation of the scan element, and may be subject to error. It is therefore desirable to provide a compact scan element that exhibits a high degree of immunity to irregular scan speed, beam shifting, unwanted tilting, misalignment, drooping, and damage.
Further drawbacks associated with conventional scan elements are radical bursts of acceleration and deceleration of the scan mirror, which distort the timing of light signals reflected from a barcode target. Distortion often occurs when a pulse of current, such as a short duty cycle square wave, is used as a drive waveform, especially at non-resonant frequencies. It is therefore desirable to have the scan element respond faithfully to a shaped drive signal, such as a triangle or sinusoidal waveform, to provide a non-jerky scan speed characteristic. It is further desirable to provide a scan mechanism that can be driven over a range of speeds below resonance at low power and controlled under the constant influence of current in a drive coil having no pole piece.